(1) Field of the Invention
The present invention generally relates to a lane change detecting system for mobile bodies such as vehicles, and more particularly to a lane change detecting system for detecting that a mobile body has gone across a boundary between adjacent lanes. In addition, the present invention relates to a mobile body detecting device employed in such system.
(2) Description of the Related Art
In recent years, an automated highway system (AHS) for vehicles has been proposed (see Japanese Laid Open Patent Application No. 8-314541). In the automated highway system, magnetic markers are placed along a lane of a road at predetermined intervals and a magnetic sensor provided in a vehicle which runs on the road detects the magnetic markers. Steering control of the vehicle is performed based on detecting signals from the magnetic sensor so that the vehicle does not go out of the lane. As a result, the vehicle is automatically controlled so as to run within the lane. In addition, vehicles which are running tandem communicate with each other by radio about information regarding the distance between vehicles (vehicle-vehicle communication). In each vehicle, the running speed is controlled based on the received information so that the distance between the vehicles is maintained at a predetermined value. Further, the vehicles which are automatically controlled as described above communicate by radio with communication terminals placed along the road about information regarding road conditions (vehicle-roadside communication). In each vehicle, based on the received information, the running speed is roughly controlled and driving control for avoiding danger is performed.
In such an automated highway system for the vehicles, for example, one of lanes of an express-highway is used as a special lane for the vehicles (hereinafter, referred to as automatic driving vehicles) which are automatically driven based on the information received in the vehicle-vehicle communication and the vehicle-roadside communication, or a special road (e.g., the express-highway) is provided for the automatically driven vehicles is provided. That is, the automatically driven vehicles and normal vehicles which are not automatically driven vehicles are not mixed in the same lane or the same express-highway.
However, it is difficult to provide the special lane for the automatically driven vehicles on the express-highway or the special road for the automatically driven vehicles. Thus, the automated highway system should be constructed under a condition in which the automatically driven vehicles and the normal vehicles can be mixed. In this case, the driving control of each of the automatically driven vehicle has to be based on the existence of the normal vehicles. That is, it is necessary to detect that normal vehicles have entered and exited the special lane for the automatically driven vehicles.